Apparatus for heating fluids

ABSTRACT

The apparatus described herein uses a disc wafer-type rotor featuring channels disposed around its circumference and around the interior circumference of the rotor housing specifically to induce cavitation. The channels are shaped to control the size, oscillation, composition, duration, and implosion of the cavitation bubbles. The rotor is attached to a shaft which is driven by external power means. Fluid pumped into the device is subjected to the relative motion between the rotor and the device housing, and exits the device at increased temperature. The device is thermodynamically highly efficient, despite the structural and mechanical simplicity of the apparatus. Such devices accordingly provide efficient, simple, inexpensive, and reliable sources of distilled potable water for residential, commercial, and industrial use, as well as the separation and evaporation of other liquids.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/475,351 filed May 18, 2012, which claims priority to provisionalapplication Ser. No. 61/488,061 filed May 19, 2011 under 35 U.S.C. §119(e), both of which are expressly incorporated herein by reference intheir entirety.

BACKGROUND OF THE INVENTION

The present invention is an apparatus for heating liquids using a rotorand housing featuring indentations therein that induce cavitationbubbles in the liquid. The heat generated when these bubbles rapidlycollapse is transferred to the fluid. Thus, the apparatus permitsefficient heat transfer to a fluid without a solid heat exchangerinterface.

There are a variety of devices that use mechanical energy to increasethe temperature and/or pressure of fluids. Some of these prior artdevices heat the fluid through friction between the fluid and the wallsof a rotor and housing. In other prior art designs, mechanical agitationof the liquid generates heat. U.S. Pat. No. 3,791,349 to Schaeferdiscloses an apparatus to produce steam pressure by inducing shock wavesin a distended body of water. U.S. Pat. No. 4,277,020 to Grenierdescribes a rotor and housing assembly where fluids are heated byshearing and friction between the walls of a rotor and housingcontaining circumferential indentations. Prior patents to the inventorof the present disclosure disclose a method of heating fluids throughthe production of shock waves in the liquid, where shock waves areinduced by pumping a liquid into an enclosed chamber and spinning arotor containing cylindrically-shaped dead-end bores. Venturi tubes arealso used to induce cavitation in liquids.

Mechanically-induced cavitation is a well-known phenomenon, firstencountered in the late 19th century during investigations into shippropeller design. Rapid motion of propeller blades through waterproduces a low-pressure region near the surface of the propeller bladethat results in transient bubbles being formed: a process now known ascavitation. The subsequent rapid implosion of cavitation bubbles causedby the high ambient water pressure results in the generation of enormousturbulence, heat, and pressure. The temperature generated during thecollapse of a cavitation bubble can exceed 5000 degrees Celsius.

Although cavitation is generally undesirable in marine propulsionapplications, various devices have been employed for the last few yearsfor the production and implosion of cavitation bubbles for research inultrasound, acoustical cavitation for chemical processes and relatedfields.

The apparatus described herein is intended for applications in fluidpurification, distillation, and even pasteurization. Conventionaltechnologies for purification, distillation, and pasteurizationtypically involve direct heating of a fluid. In direct heating, heatexchange occurs at a solid interface between a heat source and thesubject fluid. In other words, as a fluid flows through a heatexchanger, heat is transferred to the fluid via direct contact betweenthe fluid and the wall of the heat exchanger. However, direct heatinghas a number of disadvantages. First, direct heating results in heatexchanger scaling or coking. This necessitates relatively frequentmaintenance to remove the scaling or coking. In the pasteurizationcontext, direct heating can result in scorching and destruction of theproduct to be pasteurized.

SUMMARY OF THE INVENTION

The present invention solves these problems because usingcavitation-induced heating eliminates the heat transfer interface; heattransfer occurs directly within the fluid. The apparatus disclosedherein purifies fluids through distillation by mechanically generatingcavitation in order to heat the fluid. When the cavitation bubblescollapse, the heat generated is transferred to the fluid directly.

Cavitation-induced heating has a number of advantages in heating fluids.In the petroleum industry, cavitation-induced heating allows petroleumproducts to be heated directly in storage tanks in the field, onpipelines, or on barges to facilitate pumping and unloading in coldweather, and heavy oil products could be heated for processing withoutheat exchanger scaling. In ethanol production, cavitation-inducedheating eliminates the need for a steam boiler and allows up to foursteps in the distillation process to be combined, which reducesproduction time and cost. In dairy production, cavitation-inducedheating results in reduced maintenance, since pasteurization would occurwithout direct contact between the milk and a heat exchanger surface.This is particularly beneficial in the pasteurization of high fat dairyproducts. Cavitation-induced heating has also shown promising ability ingenerating relatively high concentrations (up to 40%) of hydrogenperoxide (H₂O₂) from tap water. A potential medical application of theapparatus described herein destroys pathogens though cavitation-inducedheating of blood or other bodily fluids.

One of the most popular current applications, however, is use ofcavitation-induced heating to purify polluted water throughdistillation. Cavitation-induced heating systems have been used inpurifying glycol-tainted water used in airport de-icing operations.Another application is purifying water that has been used in hydraulicfracturing (or “fracking”) operations used in natural gas productionfields. The water used to fracture natural gas bearing rock, or “fracwater”, is usually contaminated with sulfur and other minerals duringthe process and requires treatment before its return to the environment.A block diagram of a typical system is shown in FIG. 7, in which aself-contained, easily movable 40-foot trailer houses the cavitationgenerators, motors, and other components described below.

Another potential application of cavitation-induced heating ispurification of seawater. Current sea water distilling technologytypically uses electricity to generate heat. However, energy is lostgenerating steam to produce the electricity, and additional energy islost in transmitting electricity to the desalinization plant. However,using cavitation-induced heating would be extremely efficient inconverting seawater into steam. As the steam is condensed back across alow pressure-condensing generator, both potable water and electricitycould be produced.

The preferred embodiment of the present invention uses a shaft-driven,disc wafer type rotor (for easy modification for size and productiondesign) rotating at relatively high speed (1600-4000 RPM) within ahousing to mechanically generate cavitation bubbles in a fluid beingpumped through the cavity within the housing past the spinning rotor.The shaft may be driven by electric motor, combustion engine, windmills,animal power or other motive means known to the art. Both the rotor andthe housing have non-cylindrical shaped irregularities which inducecavitation. Unlike the systems described in the prior patents to theinventor of the present disclosure, which had cylindrical shapeddead-end bores in the rotor only, the embodiments described hereingenerate cavitation using indentations running across both the rotor andthe interior surface of the housing, as shown in FIGS. 2-6. Theseindentations will be described in greater detail below; however, thegeneral principle is that as fluid flows past indentations in the rotor,low pressure regions are generated, resulting in the formation oftransient cavitation bubbles. When these transient bubbles collapse,heat is imparted directly to the fluid. Heat is therefore rapidlygenerated and transferred to the fluid without heat transfer having tooccur between the fluid and a surface.

It is therefore an object of the present invention to provide a devicefor heating a fluid using a rotor and a stationary housing, which deviceis structurally simple with reduced manufacturing and maintenance costs.Maintenance costs are reduced because, in one preferred embodiment,seals are located on only one side of the generator. Mechanical sealstypically are the most maintenance-intensive components of the system,requiring frequent replacement. Prior designs by the inventor of thepresent disclosure included bearing and seal assemblies on both sides ofthe shock generator unit; however, the current design only has bearingsand seals on one side.

It is an additional object of the present invention to produce amechanically elegant and thermodynamically highly efficient means forincreasing pressure and/or temperature of fluids such as water(including, where desired, converting fluid from liquid to gas phase).

It is an additional object of the present invention to provide a systemfor generating and imparting heat within a fluid for residential,commercial and industrial applications, using devices featuring amechanically driven cavitation-inducing rotor and housing.

Other objects, features and advantages of the present invention willbecome apparent with reference to the remainder of this document.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric rendering of the components of a cavitation-baseddistillation system.

FIG. 2 shows an isometric rendering of the cavitation generator unit andmotor, with a cutaway view of the cavitation generator showing theirregularities in the rotor and rotor housing.

FIG. 3 shows a cross sectional cutaway view showing the cavitationgenerating irregularities of the rotor and rotor housing.

FIG. 4 shows an embodiment of the cavitation generator having smoothlycurved channels in the circumference of the rotor and the rotor housing

FIG. 5 shows another embodiment of the cavitation generator havingangular, square-shaped channels in the circumference of the rotor andthe rotor housing.

FIG. 6 shows another embodiment of the cavitation generator having openpolygonal shaped channels in the circumference of the rotor and therotor housing.

FIG. 7 is a system block diagram of an application of the invention usedto purify waste water byproducts from hydraulic fracturing operationsused in natural gas production.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the overall configuration of the preferred embodiment of asystem 20 designed to purify contaminated water, such as frac water, inbatches. The contaminated fluid is first pumped into tank 8. From thetank, the fluid passes through tank outlet line 17 to the inlet ofcavitation generator 1. As shown in FIG. 2 and as described above, thecavitation generator consists of two primary parts, a rotor housing 4and a rotor 5. The rotor 5 is driven by a shaft 3 that is coupled to amotor 2. In the preferred embodiment, an electric motor is used. Thesize of the motor is dependent on the size of the unit; typically, 500or 1000 horsepower motors would be used for applications requiringpurification of up to 100,000 gallons per day. One skilled in the artwill realize that any type of motive power capable of providing torqueto a shaft can be substituted for an electric motor, although in thesecases additional mechanical complexity may be required in the form ofgears to match motor speed with the desired rotor rotational speed(typically 1600-4000 RPM).

The speed of the rotor is one of several variables involved in inducingcavitation. Typically, the outer edge of the rotor indentations (i.e.the tips shown in FIGS. 3-6) must have a speed of at least 90 feet persecond to induce cavitation in frac water, so the smaller the rotordiameter, the larger the RPM required to generate the required tipspeed, and vice versa. The RPM range given above was found to besufficient for rotors ranging in size from 5 inches in diameter to 36inches in diameter.

As contaminated fluid passes from tank 8 into the inlet of thecavitation generator 1, it fills a cavity between the rotor 5 and therotor housing 4 as shown in FIG. 3. For applications involving fracwater, the gap between the rotor and housing is 0.250 inches. This gap,however, varies with the type of fluid designed to be heated. Theexterior of the rotor and the interior of the housing containindentations that are designed to maximize cavitation in the fluidflowing through the cavitation generator.

As shown in FIG. 3, these indentations may be inclined into or away fromthe direction of rotation. The angle of inclination of the indentationseither into or away from the flow and the depth of the indentationsthemselves will depend on the nature of the fluid to be heated. FIGS. 3,5-6 shows indentations that are defined by the intersection of planarsurfaces, while FIG. 4 shows indentations that are curved.

Cavitation bubbles are generated as the low-pressure boundary layer ofthe water in contact with the surface of the rapidly spinning rotor isswept over the lip of the indentations. This is similar to water flowingaround a sharp bend in a pipe, where the pressure on the outside(concave wall) of the curve is higher than that on the inside (convexwall), where cavitation can occur. In the pipe the bubbles would becarried away by the movement of the fluid, but in the present inventionthe rotor indentations' shape and depth act to fix the location of thecavitation bubbles until the bubbles implode generating heat which isimmediately imparted to the fluid. Additionally as the harmonics of thedevice come into play the bubbles began to oscillate and continue toreform and collapse. Bubble size and collapse are the results of thespecifics of the irregularities and rotor design, causing millions ofcavitation bubbles to form and collapse simultaneously. The heatgenerated by the collapsing bubbles is imparted directly to the fluid.

The depth, shape, and number of these indentations, their inclinationrelative to the fluid flow, the speed of the outer part of the rotor(i.e. the tip), as well as the amount of time the fluid spends insidethe cavitation generator determine how effective the cavitationgenerator is at generating heat. These variables depend upon the natureof the fluid to be heated. The viscosity of the fluid is a major factorin optimizing the design of the rotor and housing. Higher viscosityfluids are generally more resistant to the formation of cavitation. Allof the current embodiments feature indentations in both the rotor andthe interior housing, which tend to increase the shear and therefore areideally suited to counteract viscosity effects in the fluid.

Contaminated fluid pumped into cavitation generator 1 flows past therotor, which is moving at high speed relative to the fluid. Hydrodynamicflow patterns over the irregularities described above in the rotor andhousing result in low pressure regions in the indentations, which causesthe rapid formation and collapse of cavitation bubbles, resulting inheat which is then transferred to the fluid. The heated fluid passes outof the cavitation generator 1 and back into tank 8 through tank inletline 9. The temperature differential between the inlet and outlet of thecavitation generator is measured by water inlet temperature sensor 18and water outlet temperature sensors 19 and displayed on panel 6. Thecontaminated fluid is recirculated between tank 8 and cavitationgenerator 1 until the fluid in the tank begins to vaporize. Pressure inthe system is maintained by recirculation pump 7. In the preferredembodiment, recirculation pump is a centrifugal pump driven by a 1horsepower electric motor controlled from control panel 10.

As fluid continuously circulates from tank 8 to the cavitation generator1 and back, the temperature of the fluid rises until steam is producedin tank 8. The steam produced from the contaminated fluid in the tankpasses through the top of tank 8 into steam supply line 12 and then intoheat exchanger 13. In heat exchanger 13, the steam condensed and passesthrough condensate outlet line 15 and is collected. The collected fluidhas now been purified and can be returned to its source. Cooling waterfrom an outside source, such contaminated frac water as shown in FIG. 7,is provided to the system through heat exchanger cooling water inlet 14.Power to the recirculation pump 7 is controlled at panel 10, systemtemperatures are displayed on panel 6, and power is provided throughpower box 11.

The fluid purification system described above processes contaminatedfluid in batches. Once the level of the contaminated fluid in the tankdecreases to a certain level, additional fluid is added. At the end ofthe purification process, remaining liquid in tank 8 is drained throughtank drain valve 16.

Prior art cavitation generators by the inventor of the presentdisclosure used cylindrical dead-end bores in the rotor to generateshock waves in the fluid. However, it was discovered that cavitationeffects were enhanced by modifying the prior design in two ways.

First, the prior patents to the inventor of the present disclosure onlydisclose cylindrical indentations disposed around the circumference ofthe rotor. However, the current invention uses linear or curvilinearchannels in the inner surf ace of the rotor housing that are similar to,and complimentary with, similar channels on the rotor's circumference.It was discovered that the presence of channels in the inner surf ace ofthe housing as well as on the rotor increases shear in the fluid,encouraging turbulence and greatly enhancing cavitation and water hammereffect. As explained above, cavitation is desirable in this applicationbecause the rapid formation and violent collapse of cavitation bubblesgenerated results in significant heat being generated internally in thefluid.

Second, instead of cylindrical dead-end bores disposed around thecircumference of the rotor, the channels in the rotor's circumferenceextend across the width of the rotor, which results in increased surfacearea exposed to the fluid. In certain preferred embodiments shown inFIGS. 2, 3, 5 and 6, when viewed in cross section, the channels have oneor more angular corners defined by two or more intersecting planarsurfaces in the rotor where the linear intersection of these twosurfaces is oriented generally parallel to the rotor's rotational axis.In other embodiments, however, the channels have smoothly curved wallsending with a discontinuity at the tip, such as those shown in FIG. 4.

Initial test results indicate that the currently disclosed design ismore efficient than prior art models. Distilling units using designsdisclosed herein are approximately 30% smaller than prior art unitsbased on the earlier cylindrical dead-end bore design, for the sameamount of distilling capacity.

Other rotor and housing embodiments specifically adapted for heatingcontaminated water (“frac water”) used in hydraulic fracturing(“fracking”) operations are shown in FIGS. 5 and 6. One embodiment shownin FIG. 5 has a rotor that is 8.5 inches in diameter. The rotor channelsdisposed circumferentially when viewed in cross section are rectangularwith a depth of approximately 0.75 inch and a width of approximately 0.5inch. The rotor housing is 10.5 inches in outside diameter and 9.0inches in inner diameter, and the corresponding channels in the rotorhousing are typically 0.5 inches in depth and 0.5 inches in width. Thegap between the edge of the mouth of the channels in the rotor and therotor housing is 0.25 inches.

A second rotor-rotor housing embodiment used in frac water purificationis shown in FIG. 6. The rotor is 6.75 inches in diameter, and thechannels in the rotor are defined by open pentagonal channels disposedaround the rotor's circumference as shown in FIG. 6. The bottom of thechannels are typically square, with 0.5 inches on a side, with thechannels flaring out at an angle to the outer circumference of the rotor(i.e. the tip of the tooth attached to the rotor). The outer diameter ofthe rotor housing is 10.5 inches and the inner diameter is 7.25 inches,leaving a gap of 0.25 inches between the tip of the pentagonal teeth ofthe rotor and the mouth of the channels in the rotor housing.

Also, it should be noted that although the rotor herein may becylindrical, the rotor used in the preferred embodiments is a disc-wafertype rotor i.e., a flat disc with thickness less than its diameter, asopposed to the cylinder-shaped rotor disclosed in the prior patents tothe inventor of the present disclosure. In the embodiments shown inFIGS. 5 and 6, the width of the rotor is 1.5 inches and the outsidewidth of the rotor housing is 1.875 inches.

Yet another embodiment that is a working prototype for a full-scalesystem features a 9.5 inch diameter rotor that is 1 inch wide. The rotoris driven with a 25 horsepower motor to 4000 RPM. Such a prototype haspurified 6.75 gallons of water per hour. A larger embodiment that isalso a working prototype has a 28 inch diameter rotor which is 3 incheswide. the rotor is driven by a 125 horsepower diesel engine at 1800 RPMand distills 20 gallons of water every 2 hours and 20 minutes.

Another, large-scale embodiment of the system that is used to reclaimcontaminated frac water is shown in FIG. 7. Return water from thefracturing process is pumped through a pre-screen filter 21, then into amixing tank 22 where it is mixed with ozone from an ozone generator 23.The ozone-treated water from mixing tank 22 is then pumped to a 40 footlong container 24 housing the system 20 described above and shown inFIG. 1. The heated water is sent through a high-pressure jet pump 25, asand bed filtration system 26, and then to heat exchanger 27. In heatexchanger 27, the steam is condensed through heat exchange with returnwater from the fracturing process. The return water is therebypre-heated before it passes through pre-screen filter 21. The condensedwater is then stored in a separation tank 28, before being eitherdischarged to the environment or reused in the fracking process.

What is claimed is:
 1. An apparatus for inducing cavitation in a fluid in order to heat said fluid, said apparatus comprising: a rotor having a rotor axis, a width extending parallel to the rotor axis, and a first set of indentations disposed in a first surface and spaced substantially around its circumference, wherein each indentation of the first set of indentations extends along the entire width of the rotor and parallel to the rotor axis; wherein a diameter of the rotor is greater than the width of the rotor; and a rotor housing having a second set of indentations disposed in a second surface opposing said first set of indentations, the second set of indentations extending along an axial direction of the rotor housing, the rotor being associated with the rotor housing such that the rotor rotates relative to the rotor housing so that the first and second sets of indentations pass one another as the rotor rotates relative to the rotor housing; wherein said rotor and said rotor housing define a cavity through which a fluid passes from an inlet to an outlet, wherein the size of the cavity and the shapes of the first set of indentations and second set of indentations induces cavitation in said fluid passing through the cavity as the rotor rotates relative to the rotor housing; and wherein the cavitation causes the rapid formation and collapse of cavitation bubbles, resulting in heat which is transferred to the surrounding fluid.
 2. The apparatus according to claim 1, wherein said channels of said first set of indentations and said channels of said second set of indentations are linear when viewed in cross-section perpendicular to an axis of rotation of the rotor.
 3. The apparatus according to claim 1, wherein said channels of said first set of indentations and said channels of said second set of indentations are curvilinear when viewed in cross-section perpendicular to an axis of rotation of the rotor.
 4. The apparatus according to claim 1, wherein said channels of said first set of indentations and said channels of said second set of indentations are open-ended polygons when viewed in cross-section perpendicular to an axis of rotation of the rotor.
 5. The apparatus according to claim 1, wherein said fluid is pumped through said cavity by a pump.
 6. The apparatus according to claim 1, wherein said fluid is contaminated frac water.
 7. The apparatus according to claim 6, wherein said first surface of said rotor and said second surface of said rotor housing are separated by a distance of approximately 0.250 inches.
 8. The apparatus according to claim 6, wherein the rotor and the rotor housing are configured such that the optimum cavitation generation is achieved when said rotor is rotated at 1600-4000 RPM.
 9. An apparatus for inducing cavitation in a fluid in order to heat said fluid, said apparatus comprising: a first surface having a width extending in an axial direction and a first set of indentations disposed thereon and spaced substantially around the first surface, wherein each indentation of the first set of indentations extends along the entire width in the axial direction of the first surface, wherein a diameter of the first surface is greater than the width, and a second surface having a second set of indentations disposed thereon and opposing said first set of indentations, the second set of indentations extending along an axial direction of the second surface, said first surface and said second surface being associated with one another such that said second surface is configured to move relative to said first surface so that the first and second sets of indentations pass one another, wherein the first and second surfaces define a cavity having an inlet configured to receive the fluid and an outlet, such that the fluid passes through the cavity between the inlet and the outlet, and the size of the cavity and the shapes of the first set of indentations and second set of indentations induces cavitation in said fluid passing through the cavity as the first surface moves relative to the second surface, and wherein the cavitation causes the rapid formation and collapse of cavitation bubbles, resulting in heat which is transferred to the surrounding fluid.
 10. The apparatus according to claim 9, wherein said first surface is associated with a rotor housing and said second surface is associated with a rotor, wherein said rotor housing and said rotor define the cavity.
 11. The apparatus according to claim 10, wherein said second surface is a disc-wafer shaped rotor.
 12. The apparatus according to claim 9, wherein the fluids are pumped through said cavity by a pump.
 13. The apparatus according to claim 9, wherein said fluid is contaminated frac water.
 14. The apparatus according to claim 13, wherein said first surface and said second surface are separated by a distance of approximately 0.250 inches.
 15. The apparatus according to claim 13, wherein said second surface is associated with a rotor, and the rotor is configured to rotate at 1600-4000 RPM.
 16. The apparatus according to claim 9, wherein said first set and said second set of indentations are channels forming open-ended polygons when viewed in cross-section.
 17. An apparatus for purifying polluted fluids using cavitation-induced heating of said fluid, the apparatus comprising: a cavitation generator, comprising, a rotor having a rotor axis, a width extending parallel to the rotor axis, and a first set of channels disposed in a first surface and spaced substantially around the circumference of the rotor, wherein each channel of the first set of channels extends along the entire width of the rotor and parallel to the rotor axis; wherein a diameter of the first surface is greater than the width; a rotor housing having a second set of channels disposed in a second surface around the interior circumference of the rotor housing, the second set of channels extending along an axial direction of the rotor housing, the rotor being associated with the rotor housing such that the rotor rotates relative to the rotor housing so that the first and second sets of channels pass one another as the rotor rotates relative to the rotor housing; and a motor coupled to said rotor and configured to drive said rotor; wherein the rotor and the rotor housing define a cavity having an inlet configured to receive fluid and an outlet, such that the fluid passes through the cavity via the inlet and the outlet, and the shape of said channels induces cavitation in the fluid within the cavity when the first and second sets of channels pass one another; and wherein the collapse of bubbles generated by said cavitation imparts heat to said fluid in said cavity; a steam generation tank in flow connection with the cavitation generator; a recirculation pump in flow communication with the cavitation generator; and a heat exchanger in flow communication with the steam generation tank; wherein water heated in said cavitation generator is recirculated from said cavitation generator to said steam generation tank until steam in said steam generation tank begins to vaporize.
 18. The apparatus of claim 17, wherein the first set of channels includes first channels disposed evenly around the circumference of the rotor, and the second set of channels includes second channels disposed evenly around the interior circumference of the rotor housing, and wherein the first channels and the second channels are linear when viewed in cross-section perpendicular to an axis of rotation of the rotor.
 19. The apparatus of claim 17, wherein the first set of channels includes first channels disposed evenly around the circumference of the rotor, and the second set of channels includes second channels disposed evenly around the interior circumference of the rotor housing, and wherein the first channels and the second channels are curvilinear when viewed in cross-section perpendicular to an axis of rotation of the rotor. 